Morphological characteristics of low density and high lithium content LixNi1-xO cathodes for molten carbonate fuel cells

LixNi1-xO cathode structures were prepared by solid state reaction in air of nickel and lithium carbonate powder mixtures. Density changes of Ni/Li2CO3 composites following thermal treatment at 700 degrees C were determined as a function of starting composition and isothermal time so as to evaluate the effect of Li2CO3 content in the starting mixture on the microstructure of the resulting LixNi1-xO solid solutions. Total porosity, calculated from density data, increased up to the composition with 23 at% Li+, beyond which the porosity was nearly constant. An analysis of the compositions with nominal 30 and 44 at% Li+ showed that, by Li2CO3 decomposition during isothermal treatment at 700 degrees C, both the amount and lithium atomic fraction of LixNi1-xO solid solution increased with time, but the porosity of the solid solution was unchanged. It was denoted that lithium carbonate affects lithium nickel oxide porosity by mass-to-void transformation during the reaction of Li2CO3 with LiyNi1-yO to get LixNi1-xO with x>y, and by carbon oxide and/or carbon dioxide evolution following Li2CO3 decomposition. While the specific pore volume related to mass-to-void transformation increased with Li2CO3 amount, for high lithium content solid solutions, the specific pore volume, due to gas evolution, decreased with lithium carbonate content of the mixture. (C) 1997 Elsevier Science Limited and Techna S.r.l.